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My teacher gave us a question with the diameter being equal to 8 inches, the radius is equal to 4 inches, and the approximate circumference being equal to 25.12 inches. When he says to find the approximate area he says to use 3.14 for pi but I get the same answer using the pi sign and 3.14. However I cannot find the exact circumference when I know the approximate circumference and I am having trouble finding the area of the circle (both approximate and exact). Please help me? I'm pretty sure this should be easy but I am utterly confused.

The Problem I Should Know

Nora Smith
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  • What formulae did you use for circumference and area?

    $$\text{Circumference} = \pi\times\text{diameter} =2\pi\times \text{radius}\ \text{Area} = \pi \times\left(\text{radius}\right)^2$$

     – peterwhy Jun 02 '22 at 23:26
  • Replying to peterwhy Yes. I used that formula for both but it didn't work. – Nora Smith Jun 03 '22 at 13:56
  • One question at a time: what steps would you take to calculate the exact circumference, when the diameter and the radius are given? What $\pi$ value do you use for exact calculations? – peterwhy Jun 03 '22 at 14:19
  • @peterwhy I use the pi symbol as he says but it still won't calculate. I think the answer would be 12.56 but it says it's wrong. – Nora Smith Jun 03 '22 at 15:37
  • $12.56$ is $3.14\times 4$ or about $\pi\times 4$, and $4$ inches is the radius. If we are still talking about circumference here, the formula should be

    $$\text{Circumference} = \pi\times\text{diameter} =2\pi\times \text{radius}$$

     – peterwhy Jun 03 '22 at 17:38
  • So 3.14 times 8 = 25.12 but that's the approximate so what's the exact? – Nora Smith Jun 03 '22 at 20:29
  • I think you mention in another question that you use a calculator? Try calculating $\pi\times 8$ for a more precise value? – peterwhy Jun 03 '22 at 20:32
  • The only problem is that my calculator still says the right answer but I will try again. pi times 8 equals 25.1327412287 inches correct? – Nora Smith Jun 03 '22 at 23:45
  • Nevermind. I figured this out. – Nora Smith Jun 03 '22 at 23:53

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